The present invention relates to a packaging machine for continuously producing sealed packages of pourable food products.
Machines for packaging pourable food products, such as fruit juice, wine, tomato sauce, pasteurized or long-storage (UHT) milk, etc., are known, in which the packages are formed from a continuous tube of packaging material defined by a longitudinally sealed strip.
The packaging material has a multilayer structure comprising a layer of paper material covered on both sides with layers of heat-seal plastic material, e.g. polyethylene, and, in the case of aseptic packages for long-storage products, such as UHT milk, also comprises a layer of barrier material defined, for example, by an aluminium film, which is superimposed on a layer of heat-seal plastic material and is in turn covered with another layer of heat-seal plastic material eventually defining the inner face of the package contacting the food product.
To produce such packages, the strip of packaging material is unwound off a reel and fed through a sterilizing unit, in which it is sterilized, for example, by immersion in a chamber containing a liquid sterilizing agent, normally a concentrated hydrogen peroxide and water solution.
Once the strip has been sterilized, the sterilizing agent is removed, e.g. vaporized by heating, from the surfaces of the packaging material, and the strip of packaging material so sterilized is maintained in a closed sterile environment, and is folded and sealed longitudinally to form a tube.
More specifically, the strip of packaging material is fed vertically through a number of successive forming assemblies, which interact with the strip to fold it gradually into a cylinder. More specifically, the forming assemblies comprise respective roller folding members defining a number of compulsory strip passages varying gradually in section from an open C to a substantially circular shape.
By interacting with the folding members, opposite lateral portions of the strip are superimposed one on top of the other with a ribbon of plastic material, e.g. polyethylene, in between, so as to form a tube of packaging material.
At a sealing station downstream from the folding assemblies, the superimposed lateral portions of the strip are heat sealed to each other to form a longitudinal seam of the tube of packaging material.
In other words, the resulting tube forms an extension of the aseptic chamber, and is filled continuously with the pourable food product and then sent to a forming and (transverse) sealing unit for forming the individual packages and in which the tube is gripped between pairs of jaws to seal the tube transversely and form pillow packs.
The pillow packs are separated by cutting the sealed portions between the packs, and are then fed to a final folding station where they are folded mechanically into the finished shape.
To ensure perfect transverse sealing of the tube of packaging material and correct folding of the pillow packs along respective preformed fold lines on the packaging material, the tube must be fed in a predetermined or desired angular position with respect to its own axis and to the structure of the packaging machine. In particular, when the tube of packaging material is sealed transversely by means of an ultrasonic sealing device, the seam of the tube must engage a respective groove formed in one of the elements opposing the active elements of the sealing device between which the packaging material is gripped under pressure, if not, this may result in incorrect distribution of the contact pressures between the active elements of the sealing device and the packaging material, thus impairing the quality of the seal.
On known packaging machines, the angular position of the tube of packaging material may vary, in actual use, from the desired angular position, due to the lateral edges of the strip not being perfectly straight, and due to the impact of the successive pairs of jaws on the tube.
To minimize the angular shift of the tube of packaging material with respect to the desired angular position, the folding member of one of the forming assemblies is connected to the structure of the packaging machine in angularly adjustable manner about the axis of the tube being formed, so as to enable adjustment of the angular position of the tube. This is done manually, however, by the operator at the start of the cycle and, if necessary, following routine checks of the packages coming off the machine.
The correction made by the operator therefore takes a relatively long time, normally in the region of a few minutes, which, given the high output rate of the packaging machines considered, amounts to a relatively large number of packages being rejected at the end of the cycle.
It is an object of the present invention to provide a packaging machine for producing sealed packages of pourable food products, designed to eliminate the aforementioned drawbacks typically associated with known machines.
According to the present invention, there is provided a packaging machine for producing sealed packages, containing a pourable food product, from a strip of packaging material fed along a path; said machine comprising:
a fixed structure;
a number of forming assemblies arranged successively along a vertical portion of said path and interacting with said strip of packaging material to fold the strip gradually into a cylinder and superimpose opposite lateral portions of the strip to form a tube of packaging material having a longitudinal first axis;
sealing means for sealing said lateral portions to each other to form a longitudinal seam of said tube of packaging material; and
filling means for continuously filling said tube of packaging material with said pourable food product;
at least one of said forming assemblies comprising a folding member defining a compulsory passage for said strip of packaging material being folded, and connected to said fixed structure in angularly adjustable manner about said first axis to adjust the angular position of said tube with respect to the first axis;
characterized by also comprising actuating means connected operatively to said folding member and activated selectively to rotate the folding member about said first axis; sensor means located along said vertical portion of said path, downstream from said sealing means, and generating a position signal correlated to the angular position of said seam with respect to said first axis; and control means receiving said position signal, and generating a first control signal, which is supplied to said actuating means to restore said seam to a desired angular position with respect to said first axis, in the event said position signal differs from a reference value indicating said desired angular position of said seam.